Plasters for transdermal application of medicinal active ingredients are known. Transdermal plasters are commercially available and are described in a large number of publications and patents.
In one type of transdermal plaster the medicinal active ingredients are arranged in a reservoir which is shielded from the skin with a control membrane which releases a controlled amount of active ingredient onto the skin through this membrane. A disadvantage of this arrangement is that the active ingredient, reservoir constituents and membrane must be carefully matched with one another, and consequently this system cannot be employed for all medicinal active ingredients. In addition, the production of such a plaster is expensive due to the complicated assembly of the parts.
In another type of transdermal plaster the medicinal active ingredient is incorporated into the adhesive composition of the plaster. In this case also, it is necessary for the active ingredient and adhesive composition to be carefully matched with one another. Although these systems are simpler and more economical to produce, they unavoidably result in interactions between the active ingredient and adhesive especially since as a general rule adhesives do not consist of defined individual constituents but are diverse mixtures.
German Offenlegungsschrift No. 3,202,775 describes an adhesive plaster for transdermal application of an active ingredient in which the active ingredient is printed onto the adhesive surface of the plaster in the form of separate spaced elements. Although such a plaster is economical to produce it has serious disadvantages and has not found acceptance in practice. In particular, the interactions between the active ingredient and adhesive composition impair uniform long-term release of the active ingredient through the skin because of migration, either of the active ingredient into the adhesive composition or the plasticizer or plasticizer-like substance into the active ingredient element, depending on external influences such as temperature and moisture. Such a plaster cannot fulfill the strict regulations of governmental registration as a drug especially in respect of the required storage stability under possibly adverse conditions during which migration phenomena may take place over a prolonged period.
An object of the present invention is, accordingly, to provide a medicated self-adhesive plaster for transdermal application which does not have, or has only to a substantially lesser degree, the above-mentioned disadvantages of the prior art. In particular, a plaster is provided which on the one hand can be produced economically and on the other hand is free from problems of migration of adhesives into the medicinal active ingredient and vice versa, and in addition, as far as possible, avoids any type of interaction between the two components.